// SPDX-License-Identifier: EPL-2.0 OR GPL-2.0-or-later
// SPDX-FileCopyrightText: Bradley M. Bell <bradbell@seanet.com>
// SPDX-FileContributor: 2003-22 Bradley M. Bell
// ----------------------------------------------------------------------------

# include <cppad/cppad.hpp>

bool log1p(void)
{  bool ok = true;

   using CppAD::AD;
   using CppAD::NearEqual;

   // 10 times machine epsilon
   double eps = 10. * std::numeric_limits<double>::epsilon();

   // domain space vector
   size_t n  = 1;
   double x0 = 0.5;
   CPPAD_TESTVECTOR(AD<double>) ax(n);
   ax[0]     = x0;

   // declare independent variables and start tape recording
   CppAD::Independent(ax);

   // a temporary value
   AD<double> expm1_of_x0 = CppAD::expm1(ax[0]);

   // range space vector
   size_t m = 1;
   CPPAD_TESTVECTOR(AD<double>) ay(m);
   ay[0] = CppAD::log1p(expm1_of_x0);

   // create f: x -> y and stop tape recording
   CppAD::ADFun<double> f(ax, ay);

   // check value
   ok &= NearEqual(ay[0] , x0,  eps, eps);

   // forward computation of first partial w.r.t. x[0]
   CPPAD_TESTVECTOR(double) dx(n);
   CPPAD_TESTVECTOR(double) dy(m);
   dx[0] = 1.;
   dy    = f.Forward(1, dx);
   ok   &= NearEqual(dy[0], 1., eps, eps);

   // forward computation of higher order partials w.r.t. x[0]
   size_t n_order = 5;
   for(size_t order = 2; order < n_order; order++)
   {  dx[0] = 0.;
      dy    = f.Forward(order, dx);
      ok   &= NearEqual(dy[0], 0., eps, eps);
   }
   // reverse computation of derivatives
   CPPAD_TESTVECTOR(double)  w(m);
   CPPAD_TESTVECTOR(double) dw(n_order * n);
   w[0]  = 1.;
   dw    = f.Reverse(n_order, w);
   ok   &= NearEqual(dw[0], 1., eps, eps);
   for(size_t order = 1; order < n_order; order++)
      ok   &= NearEqual(dw[order * n + 0], 0., eps, eps);

   return ok;
}

// END C++
